Hypertens Pregnancy, 2014; 33(2): 132–144 ! Informa Healthcare USA, Inc. ISSN: 1064-1955 print / 1525-6065 online DOI: 10.3109/10641955.2013.842583
ORIGINAL ARTICLE
Gabriela Ruiz-Quin ´ pez,1 ˜ onez,1 Sandra A. Reza-Lo Dora Virginia Cha ´ vez-Corral,1 Blanca Sa ´ nchez-Ramı´rez,2 Irene Leal-Berumen,1 and Margarita Levario-Carrillo1 1
Facultad de Medicina and Facultad de Ciencias Quı´micas, Universidad Auto´noma de Chihuahua, Chihuahua, Me´xico
2
Objectives: To compare maturity of placentas from women with hypertensive disorders with those from normotensive pregnancies and to determine the relationship between placental maturity (PM) and the diagnosis of small-for-gestational-age (SGA) in the newborns. Materials and methods: We examined placental stained specimens from women with normotensive pregnancies (n = 100), diagnosis of gestational hypertension (n = 38), mild (n = 10), or severe preeclampsia (n = 34) in an optical microscope. Placental Maturity Index (PMI) was calculated as the number of vasculo-syncytial membranes (VSM) in 1 mm2 divided by VSM thickness (mm). Hypermaturity was defined as >90th percentile of the PMI from placentas of normotensive pregnancies. Newborns were classified as SGA, adequate-for-gestational-age (AGA) or large-for-gestational-age (510th, 10–90th, and >90th percentile from weight for gestational age reference tables, respectively). Results: PMI in preeclamptic women (taking together mild and severe preeclampsia, PMI = 43.4 ± 1.6) was significantly higher than in normotensive women (PMI = 36 ± 2, p = 0.045). Hypermaturity was more frequent (p50.05) in placentas from women with preeclampsia than in those from normotensive women only in preterm pregnancies (537 weeks), but not in those at term (p = 0.41). The frequency of hypermaturity in placentas from women with gestational hypertension was not statistically different than in normotensive women. Hypermaturity was also more frequent in placentas from SGA (OR = 2.63, p50.05) than in AGA newborns. Conclusion: The PMI was increased in preeclampsia, but not in gestational hypertension. Placental hypermaturity was also associated with the diagnosis of SGA in newborns. PM might have a role in the relationship between maternal factors and SGA.
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Placental maturity, hypertensive disorders of pregnancy and birth weight
Keywords Birth weight, Gestational hypertension, Placental maturity, Placental maturity index, Preeclampsia, Small-for-gestational-age.
INTRODUCTION Hypertensive disorders of pregnancy, such as gestational hypertension and preeclampsia, are common and affect about 10% of pregnancies (1). They are
Correspondence: Sandra A. Reza-Lo´pez, Laboratorio de Embriologı´a, Facultad de Medicina, Universidad Auto´noma de Chihuahua, Circuito Universitario Campus II, Chihuahua, Chih. C.P. 31109, Me´xico. Tel: +52 (614) 439 1500, ext. 3572. E-mail: [email protected]
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Placental maturity and hypertensive disorders
the main cause of maternal mortality in developing countries and they are also associated with intrauterine growth restriction (IUGR), thus increasing perinatal mortality and morbidity (2–4). Several maternal, placental and fetal factors influence fetal growth and development. Maternal age, nutrition, body composition and complications during pregnancy have been associated with birth weight (5,6). Other factors related to preplacental, uteroplacental, or postplacental hypoxia, such as maternal anemia, preeclampsia or IUGR, respectively, also affect fetal growth. Because the placenta mediates nutrient transport between the mother and the fetus, the functionality of its structures plays a fundamental role for fetal growth and development (7,8). Placental morphology changes as pregnancy progresses. The proportion of syncytial knots, the number of terminal villi, and the number of vasculosyncytial membranes (VSM) gradually increase and VSM thickness decreases as the placenta matures. These changes in placental maturity (PM) are observed in placentas from non-complicated pregnancies from weeks 21 to 38 (9,10), after which PM shows a plateau (11). However, PM may be influenced by several maternal and fetal factors resulting in a delayed (hypomaturity) or accelerated PM (hypermaturity). For instance, gestational diabetes and Rhesus incompatibility have been associated with delayed PM (12), maternal smoking habit has been associated with both delayed and accelerated PM (12–14), and preeclampsia has been associated with an accelerated PM, in particular, in those with an early start of disease [33–56% in pregnancies before the 37th week vs. 4% in pregnancies at term, 37 weeks] (15–19). Furthermore, the degree of PM has been related with the severity of hypertensive disease in some studies (16,19,20). Placental accelerated maturity or placental hypermaturity (PHM) has been also observed in cases of IUGR low birth weight (15,17,18,20) associated or not with the diagnosis of preeclampsia (15). A hypermature placenta is characterized by the predominance of terminal villi and an increase in syncytial knotting, as compared to features expected for its gestational age (12). A standardized classification of placental pathology diagnosis based on its morphology has been proposed. However, there is no agreement in the literature regarding which indicator would be the best to define PHM and its relationship with clinical outcomes (21). PHM has been assessed using several measures and cut-off. For example, the number of syncytial knots above the average has been used as a marker of PHM. However, the average value was obtained from a small sample size [n = 9/10 per gestational week] (19). Other authors have assessed PHM by the predominance of small terminal over intermediate villi and syncytial knotting, but no cut-off was reported (20). Although these studies did not report the intra and inter-observer agreement, other studies have reported that the observer reliability of placental histological measures is poor (22). For example, interobserver agreement in villous maturity between five expert pathologists has been reported with a kappa value of 0.58 (23) and a kappa value 0.60 was obtained between two pathologists for the diagnosis of maturation disorders (21). Then, the placental maturity index (PMI) has been proposed as a more objective histological assessment.
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The PMI is correlated with gestational age and birth weight and takes into account the number of epithelial plates (or VSM) in terminal villi and their thickness because these two measures are directly related to PM (10). However, it is unclear whether the PMI is altered by hypertensive disorders of pregnancy and in IUGR. Therefore, the objectives of this study were: (1) To compare the PMI in placentas from women with diagnosis of gestational hypertension and preeclampsia with those from normotensive pregnancies; and (2) to determine the relationship between the PMI and the diagnosis of small-for-gestational-age (SGA) in the newborns.
MATERIALS AND METHODS Women either normotensive (n = 100) or with hypertensive disorders of pregnancy (gestational hypertension, n = 38; mild preeclampsia, n = 10; and severe preeclampsia, n = 34) were recruited from two public hospitals (Hospital General Salvador Zubira´n and Hospital Central del Estado, Chihuahua, Me´xico) for this cross-sectional study. Women with diagnosis of heart disease, neuropathy, pregestational hypertension, diabetes mellitus, hyper or hypothyroidism, eclampsia, HELLP syndrome, those with twin pregnancies, fetal death, and those with a newborn with congenital defects were not included in the study. Women accepted to participate by signing an informed consent form. The study protocol was approved by the institution ethics board. We obtained information on maternal clinical characteristics, biochemical measures and newborn anthropometry by questionnaire and from clinical records. Anemia was defined as hemoglobin concentrations 511.0 g/dl. Diagnosis of gestational hypertension, mild or severe preeclampsia was confirmed according to the Guidelines of the Mexican College of Obstetricians and Gynecologists (24). Briefly, gestational hypertension was defined as a systolic blood pressure of 140 mm Hg, or a diastolic blood pressure 90 mm Hg in women with previously normal blood pressure; mild preeclampsia was diagnosed when systolic and diastolic blood pressure were of 140 mm Hg or higher and 90 mm Hg or higher, respectively, after the 20th gestational week in women with previously normal blood pressure; and proteinuria (0.3 g protein in a 24-h specimen). Preeclampsia was considered severe when one or more of the following criteria were present: systolic blood pressure 160 or diastolic blood pressure 110 mm Hg on 2 occasions at least 6 h apart, proteinuria 2 g in a 24-h specimen or 3þ in 2 random samples at least 6 h apart, oliguria of less than 500 ml in 24 h; cerebral or visual disturbances; pulmonary edema or cyanosis; epigastric or right upper-quadrant pain, impaired liver function, thrombocytopenia, or fetal growth restriction (24). Gestational age was calculated from the date of last menstrual period and confirmed by ultrasound studies performed before the 16 weeks of gestation in 20% of the study population (intra-class correlation coefficient [ICC] = 0.89). Newborns were classified according to their birth weight and gestational age as small (510th percentile), adequate (10–90th percentile), or large (>90th percentile) for gestational age, using percentile reference tables of weight for gestational age for infants from the North of Mexico (25).
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Placental maturity and hypertensive disorders
Sample Collection and Morphometric Analysis of Placentas Immediately after birth, the umbilical cord was clamped, the maternal blood clot was removed, and the placenta collected. Placental weight and major and minor diameters were measured. A macroscopic examination was performed looking for areas of infarct, fibrin deposition and calcification (26). Placenta samples were obtained and analyzed as in previous studies (11). Briefly, samples from the central area of placentas were dissected from macroscopically lesion-free sites and were immediately fixed in a 10% formol solution, embedded in paraffin, and stained with hematoxylin and eosin. We examined stained specimens with an optical microscope (Axioscope 2 Plus, Carl Zeiss Jena GmbH, Jena, Germany), using the AxioVision software (AxioVision LE, v.4.6.2.0, Carl Zeiss MicroImaging GmbH, Germany) selecting the area of the slide without any microscopic lesion (or with the least number of lesions) for maturity measures. The number and average diameter of terminal villi [terminal villi were defined as those with diameter between 30 and 60 mm] (12) found in 1 mm2 were assessed. We obtained the average of 5 fields at a 5 magnification. In photomicrographies of each slide, we measured the following: number of VSM (identified in the external sites of the villi, as nuclei- and knotting-free areas), the thickness of VSM in the thinnest part of the transversely cut surface of the terminal villi and the diameter of capillaries, with a 40 magnification. The average of these measurements in 10 terminal villi was calculated. We calculated the PMI as the number of VSM divided by the average of their thickness (10). All placenta measures were carried out by an observer, blinded to the participant diagnosis. The values of ICC calculated to evaluate intra-observer agreement were: 0.88 for the VSM thickness, 0.97 for the number of VSM, and 0.98 for the number of terminal villi. Statistical Analyses Data are presented as means and standard deviation or frequency and proportion depending on the variable measuring scale, unless otherwise indicated. The sample size of the group with diagnosis of mild preeclampsia was small (n = 10), therefore we also carried out analyses taking together both mild and severe preeclampsia groups. Group means were compared by one-way ANOVA. Log-transformed variables or Kruskal–Wallis test were used when the variables were not normally distributed. Differences in variables measured in nominal scale were analyzed by 2 test or Fisher’s exact test. To evaluate PHM, we took as a cut-off the 90th percentile of the PMI distribution in the normotensive group with newborn AGA considering gestational age (preterm 537 week; term 37 weeks). The PMI cut-off was 53 for preterm pregnancies placentas, and 68, for those at term. Logistic regression models were used to determine the association between PHM and hypertensive disorders and with SGA outcome, and odds ratios (OR) were calculated. We tested the potential effect of other biological or statistically significant variables by multivariate analyses. Stata, v. 11.0 (Stata Statistical software, Release 11.0, College Station, TX: stata) was used for data analyses.
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RESULTS Characteristics of the studied groups were not statistically different, except in the number of years of education (Table 1). Table 2 shows the morphological characteristics of placentas by study group. The number of VSM was greater in placentas from the severe preeclampsia group, compared with the normotensive group. There was a trend towards a smaller diameter of terminal capillaries in placentas from the gestational hypertension group and a higher PMI in the severe preeclampsia group, compared with placentas from normotensive women. A higher proportion of placentas with infarct areas was observed in hypertensive disorders than in the normotensive group (Table 2). PMI in preeclamptic women (taking together mild and severe preeclampsia, PMI = 43.4 ± 1.6) was significantly higher than in normotensive women (PMI = 36 ± 2, p = 0.045). The correlation between the PMI and gestational age by diagnosis group was as follows: in normotensive women, r = 0.25, p = 0.01; in women with diagnosis of gestational hypertension r = 0.02, p = 0.92; and in women with preeclampsia, r = 0.34, p = 0.03. PHM was associated with early gestational age within women with preeclampsia; however, this relationship was not statistically significant in placentas at term (Table 3). Placentas obtained before week 37 from women with hypertensive disorders were characterized by a thinner VSM and an increased vascularity of terminal villi compared to placentas from normotensive women (Figure 1). Placentas from women with severe preeclampsia were more likely to have hypermaturity than those from the normotensive group. Similarly, placentas from newborns that were SGA were more likely to be hypermature compared to those from AGA newborns (Table 4). The magnitude of the association was similar and remained statistically significant, after adjusting the model for potential confounders, none of which resulted significant in the multivariate analysis. Newborns from women with severe preeclampsia were lighter at birth (median and interquartilar range [IQR], 2863 g [2313–3073 g]) than those born to normotensive women (3100 g [2729–3481 g]). Birth weight was not different in newborns from gestational hypertension and mild preeclampsia groups (3150 g [2894–3530 g] and 3280 g [3084–3528 g], respectively). Birth weight of newborns from women with severe preeclampsia and hypermature placentas was 2640 g (IQR 1310–2825 g) vs. 2975 g (IQR 2975–3155 g) in those without PHM (p = 0.045).
DISCUSSION The findings of this study partially support the hypothesis that hypertensive disorders of pregnancy increase PM. PHM was mainly found in placentas from women with preeclampsia but not in those with gestational hypertension. We also show that placentas from SGA newborns are more likely to be hypermature than those from AGA newborns. Consistent with others, we found that PHM is more frequent in women with preeclampsia. Tache´ et al. found PHM in 40 and 50% of cases of mild and
b
24 ± 7 20 (53) 18 (47) 39 ± 2 9±4 3 (8) 35 (92) 26 ± 4
40 (40) 60 (60) 38 ± 3 10 ± 3
8 (8) 92 (92) 24 ± 5
Mean ± SD/n (%)
Gestational hypertension, n = 38
23 ± 6
Mean ± SD/n (%)
Kruskal–Wallis test was used. Body mass index = weight/heigth2.
a
Maternal age (years)a Parity Primiparous Multiparous Gestational age (weeks)a Education (years) Smoking during pregnancy Yes No Pregestational BMIa,b (kg/m2)
Variable
Normotensive, n = 100
Table 1. Clinical characteristics of the studied groups.
1(10) 9 (90) 24 ± 3
7 (70) 3 (30) 39 ± 1 12 ± 5
22 ± 5
Mean ± SD/n (%)
Mild preeclampsia, n = 10
3 (9) 31 (91) 25 ± 6
20 (59) 14 (41) 37 ± 4 8±4
22 ± 6
Mean ± SD/n (%)
Severe preeclampsia, n = 34
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0.17
0.97
0.09 0.04
0.11
0.36
p
Placental maturity and hypertensive disorders
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552 ± 113 19.9 ± 2.8 15.8 ± 1.9 38 ± 1 1.1 ± 0.1 19 ± 1 47 ± 2 16 ± 1 37 ± 1 7 (18) 31 (82) 7 (18) 31 (82) 1 (3) 37 (97)
7 (7) 93 (93) 20 (20) 80 (80) 3 (3) 97 (97)
Mean ± SD/n (%)
540 ± 130 18.0 ± 3.3 15.4 ± 2.7 36 ± 1 1.0 ± 0.1 19 ± 1 46 ± 2 18 ± 1 36 ± 2
Mean ± SD/n (%)
Gestational hypertension, n = 38
b
Variables were log-transformed for analyses and geometric means and SD are presented. p50.05 compared with normotensive group. c VSM = vasculosyncytial membrane. d Kruskal–Wallis test was used. e PMI = number of VSM/thickness of VSM (mm).
a
Weight (g) Major diameter (cm) Minor diameter (cm) Number of VSMc (villi/mm2)a Thickness of VSMc (mm) Number of terminal villi (in 1 mm2)a Terminal villi diameter (mm)d Terminal capillaries diameter (mm)a Placental maturity index (PMI)a,e Infarcts Yes No Fibrin deposition Yes No Calcification Yes No
Variable
Normotensive, n = 100
Table 2. Morphometric analysis of placental tissue of the studied groups.
0 (0) 10 (100)
0 (0) 10 (100)
2 (20) 8 (80)
628 ± 116 19.5 ± 2.7 17.1 ± 1.8 38 ± 1 1.0 ± 0.2 19 ± 1 46 ± 2 19 ± 1 38 ± 2
Mean ± SD/n (%)
Mild preeclampsia, n = 10
0 (0) 34 (100)
12 (35) 22 (65)
9 (26) 25 (74)
519 ± 150 17.9 ± 3.1 15.4 ± 2.6 46 ± 1b 1.0 ± 0.1 21 ± 1 46 ± 2 18 ± 1 45 ± 2
Mean ± SD/n (%)
Severe preeclampsia, n = 34
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0.86
0.08
0.01
0.13 0.32 0.17 0.01 0.69 0.32 0.52 0.07 0.06
p
138 G. Ruiz-Quin ˜ onez et al.
Placental maturity and hypertensive disorders Table 3. Placental hypermaturity by diagnosis group in preterm and term pregnancies. Placental maturity index
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Group Preterm pregnancies (537 weeks) Normotensive Gestational hypertension Preeclampsiaa Term pregnancies (37 weeks) Normotensive Gestational hypertension Preeclampsiaa a
90th percentile, n (%)
>90th percentile, n (%)
23 (92) 3 (100) 7 (50)
2 (8) 0 (0) 7 (50)
50.01
67 (89) 33 (94) 25 (83)
8 (11) 2 (6) 5 (17)
0.41
p
Including both, mild and severe preeclampsia.
Figure 1. Photomicrographs of central area tissue from preterm placentas (gestational age 537 weeks). Study groups: (A) normotensive, (B) gestational hypertension, (C) mild preeclampsia and (D) severe preeclampsia. Magnification of 5 (1) and 40 (2). VSM were identified as nuclei- and knotting-free areas in the external sites of the villi. The thickness of the VSM in the thinnest part of the transversely cut surface terminal villi and the diameter of capillaries were measured. VSM were more abundant and thinner in samples of placental tissue from hypertensive groups than in those from normotensive pregnancies. VSM, vasculo-sincitial membrane; Tvsm, thickness of vasculosincitial membrane; TV, terminal villous; V, villous vessels.
severe preeclampsia, respectively, compared to 12.7% in the control group (19) and Moldenhouer et al. (20) observed PHM in 32.9% of women with preeclampsia vs. 4.5% in normotensive women. In our study, PHM was found in 27% of placentas from women with preeclampsia and 10% in those from normotensive women. Differences in the magnitude of the reported proportions may arise from differences in the criteria and cut-off used to define PHM. Tache´ et al., determined PHM as those placentas with a syncityal knots number above the average (19), Moldenhauer et al. determined PHM according with the predominance of terminal villi over the intermediate villi and the syncytial knots number (20), and we used the 90th percentile of the PMI. In our study, the number of VSM was greater and a higher proportion of
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G. Ruiz-Quin ˜ onez et al. Table 4. Relationship between placental hypermaturity, hypertensive disorders and selected factors.
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Variable
PMI 90th percentile, n(%)
PMI >90th percentile, n(%)
Group Normotensive 90 (90) 10 (10) Gestational hypertension 36 (95) 2 (5) Mild preeclampsia 8 (80) 2 (20) Severe preeclampsia 24 (71) 10 (29) Gestational age (weeks) 537 33 (79) 9 (21) 37 125 (89) 15 (11) Smoking habit (number of cigarettes per day) 0 133 (88) 19 (12) 1–3 15 (94) 1 (6) 4 10 (71) 4 (29) Anemia Yes 19 (95) 1 (5) No 130 (86) 22 (14) Parity Primipaurus 71 (84) 14 (16) Multiparous 87 (90) 10 (10) Maternal age (years) 520 51 (88) 7 (12) 20–25 58 (87) 9 (13) 26 49 (86) 8 (14) Newborn small for gestational agea Yes 28 (76) 9 (24) No 119 (89) 14 (11) a
OR
CI95%
p
1.0 0.50 2.25 3.75
0.10–2.40 0.42–12.09 1.40–10.05
0.39 0.35 0.01
2.27 1.0
0.91–5.65
0.08
1.0 0.47 2.82
0.06–3.74 0.80–9.90
0.47 0.11
0.31
0.04–2.44
0.27
1.71
0.72–4.09
0.22
0.88 1.0 1.05
0.31–2.55
0.82
0.38–2.93
0.92
1.07–6.95
0.04
2.73 1.0
Excluding large for gestational age newborns.
VSM above the average number was observed in the group of severe preeclampsia. Because accumulation of nuclei is often observed directly lateral to the VSM (27), it is possible that the proportion of syncytial knots maybe related to the number of VSM, then we could speculate that their number might be also increased in placentas from preeclamptic women, but this remains to be confirmed. We also observed that the absolute number of terminal villi in 1 mm2 did not differ between groups. As the placenta matures, the proportion of terminal villi increases whereas the VSM thickness decreases. Thus, the PMI could be a precise indicator of villous maturity, because it takes into account the number of VSM of terminal villi and their thickness (10,11), in which the VSM thickness may serve as a proxy of VSM maturity. Furthermore, using the 90th percentile as a cut-off may identify the most severe cases of placenta hypermaturity. Further research is needed to compare these measures and to establish the most appropriate cut-off. The frequency of PHM in the group of gestational hypertension was not different from normotensive women. Although the reason for this is unclear, we could speculate that might be related to differences in the clinical course of hypertensive disorders. Whereas patients with gestational hypertension tend to present a benign evolution and similar perinatal outcomes than
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Placental maturity and hypertensive disorders
non-complicated pregnancies, patients with preeclampsia present a more severe clinical course, for both, the mother and the fetus, and they often have adverse perinatal outcomes (28). Differences in factors related to placenta growth and development, such as the vascular-endothelial growth factor, placental growth factor (PIGF), the soluble fms-like tyrosine kinase-1 (sFlt-1) and angiopoietins, might be also part of the mechanism explaining these differences. Women with low level of PIGF and high level of sFlt-1 exhibit alterations in placental development and have an increased risk of pregnancy complications such as preeclampsia (19,29,30). Alterations in these factors are less pronounced in women with gestational hypertension than in preeclampsia (31,32). However, the potential role of these factors to explain differences in PM in hypertensive disorders requires further investigation. PM has been related to several maternal factors, such as gestational age, maternal age, parity, anemia, and smoking habit, but none of them reached statistical significance in this study. However, there was a trend towards a higher proportion of PHM in preterm pregnancies (p = 0.08) than in those at term, and in placentas from women that smoked 4 cigarettes per day compared to those that did not smoke (p = 0.11). In the present study, we confirmed the correlation between gestational age and PMI only in the group of normotensive women but not in the groups with gestational hypertension or preeclampsia. This suggests that PM is altered in hypertensive disorders, and in particular in preterm pregnancies. This is further supported by the observation that PHM was found in 50% of placentas from women with preeclampsia in preterm pregnancies and only in 17% of placentas from women with preeclampsia who gave birth after 37 weeks. This finding is also consistent with other studies that have reported that PHM in women with preeclampsia is more frequent in preterm pregnancies than in those at term (15,18,20). Furthermore, an early start of hypertensive disorders could have been the reason for preterm birth (12,20) and may be related to characteristics of an accelerated PM. Several studies have shown that maternal smoking habit influences PM. However, the direction of this association has been inconsistent. For instance, some studies using the proportion of syncytial knots as a marker of PM have found degenerative changes and premature aging of placentas from women who smoke (13), similar to our observation that PHM tended to be more frequent in women who smoked 4 cigarettes per day. In contrast, other studies have found a decrease in vascularity and an increase on VSM thickness, which suggest hypomaturity, in placentas from women with smoking habit (14,33,34). As expected, an increased proportion of placentas from women with hypertensive disorders showed infarct areas. This observation is consistent with other studies that have reported higher proportion of infarct areas in placentas from women with preeclampsia or hypertension than in normotensive women (16,35). In this study, we also identified a relationship between SGA and PHM. Newborns born SGA had almost 3 times more possibilities of having PHM than those born with an adequate weight for their gestational age. Other studies have found a decrease in birth weight for gestational age in newborns from women with preeclampsia, but only in those that displayed accelerated
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PM features. In contrast, birth weight of newborns from women with preeclampsia in which PM was normal did not differ from birth weight of newborns of normotensive women (15–17). Our results showed that birth weight was lower in newborns from women with severe preeclampsia with or without PHM compared to those from normotensive women. However, newborns from women with preeclampsia and PHM were the lightest. Birth weight is closely related to placenta weight (36). In the present study, placenta weight from SGA newborns was 67 g lighter than in AGA newborns, after adjusting by gestational age. However, placenta weight was not different between normotensive and hypertensive groups. Other studies have found no difference in placenta weight between normotensive and hypertensive groups (37) and similar placental weight have been found in SGA newborns from women with or without preeclampsia (38). In contrast, other studies have found a low placenta weight associated to preeclampsia. In our study, PHM, but not placental weight, was related to both, small birth weight and preeclampsia, suggesting that hypertensive disorders could be associated with placental physiology without affecting its weight. However, whether or not intrauterine growth restriction and preeclampsia have additive or interacting effects on placental pathophysiology (39) warrant further investigation. Overall, the results of the study suggest that PM is altered in hypertensive disorders; particularly in placentas from women with diagnosis of preeclampsia and preterm pregnancies and that the PHM is associated with a decreased birth weight. However, the study has several limitations. First, we have small number of women with hypertensive disorders, in particular in the group of mild preeclampsia, which did not allow us to examine the PMI by gestational week and diagnosis, due to the reduced sample size; and second, gestational age was calculated from the last menstrual period and could lead to some misclassification. However, in the 20% of patients in which the ultrasound was available before the 16th gestational week, the sonographic and calculated gestational age had good agreement. In conclusion, the PMI and hypermaturity are increased in preeclampsia, but not in gestational hypertension. PHM is also related to a decrease in birth weight for gestational age. Whether accelerated PM mediates the relationship between maternal factors and pregnancy outcomes such as SGA requires further investigation. Longitudinal studies with a larger sample size to evaluate these associations in complicated and non-complicated pregnancies are necessary.
ACKNOWLEDGMENTS The authors wish to thank the Personnel of the ‘‘Hospital General Salvador Zubira´n’’ and the ‘‘Hospital Central del Estado’’ for their support in sample and data collection.
DECLARATION OF INTEREST The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.
Placental maturity and hypertensive disorders
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REFERENCES 1. Duley L. The global impact of pre-eclampsia and eclampsia. Semin Perinatol 2009; 33:130–7. 2. Tjoa ML, Oudejans CB, van Vugt JM, et al. Markers for presymptomatic prediction of preeclampsia and intrauterine growth restriction. Hypertens Pregn 2004;23: 171–89. 3. Huppertz B. Placental origins of preeclampsia: challenging the current hypothesis. Hypertension 2008;51:970–5. 4. Yayla M. Maternal mortality in developing countries. J Perinat Med 2003;31: 386–91. 5. Levario-Carrillo M, Rodriguez N, Tufino-Olivares E, et al. Body composition of women with newborns who are small for gestational age. Neonatology 2009;95: 15–22. 6. Sacks DA. Determinants of fetal growth. Curr Diab Rep 2004;4:281–7. 7. Jones HN, Powell TL, Jansson T. Regulation of placental nutrient transport– a review. Placenta 2007;28:763–74. 8. Mayhew TM. Enhanced fetoplacental angiogenesis in pre-gestational diabetes mellitus: the extra growth is exclusively longitudinal and not accompanied by microvascular remodelling. Diabetologia 2002;45:1434–9. 9. Loukeris K, Sela R, Baergen RN. Syncytial knots as a reflection of placental maturity: reference values for 20 to 40 weeks’ gestational age. Pediatr Dev Pathol 2010;13:305–9. 10. Janowiak Z, Mazerski J. New criterion of placental barrier maturity. Zentralbl Gynakol 1992;114:292–5. 11. Acosta-Maldonado B, Sanchez-Ramirez B, Reza-Lopez S, Levario-Carrillo M. Effects of exposure to pesticides during pregnancy on placental maturity and weight of newborns: a cross-sectional pilot study in women from the Chihuahua State, Mexico. Hum Exp Toxicol 2009;28:451–9. 12. Benirschke K, Kaufmann P. Classification of villous maldevelopment. In: Benirschke K, Kaufmann P, eds. Pathology of the human placenta, 4th ed. New York (NY): Springer-Verlag New York, Inc.; 2000:437–60. 13. Ashfaq M, Janjua MZ, Nawaz M. Effects of maternal smoking on placental morphology. J Ayub Med Coll Abbottabad 2003;15:12–5. 14. Rodriguez-Moran M, Levario-Carrillo M, Gonzalez JL, et al. Placental immaturity and hyperinsulinaemia in full-term newborns. Eur J Clin Invest 2007;37: 529–34. 15. Egbor M, Ansari T, Morris N, et al. Morphometric placental villous and vascular abnormalities in early- and late-onset pre-eclampsia with and without fetal growth restriction. BJOG 2006;113:580–9. 16. Romero-Gutie´rrez G, Vela´squez-Maldonado HA, Me´ndez-Sashida P, et al. Alteraciones histopatolo´gicas placentarias en la hipertensio´n gestacional. Ginecol Obstet Mex 2008;76:673–8. 17. Mehrabian F, Mohammadizadeh F, Moghtaderi N, Najafian A. Comparison of placental pathology between severe preeclampsia and HELLP syndrome. Arch Gynecol Obstet 2012;285:175–81. 18. Stevens DU, Al-Nasiry S, Bulten J, Spaanderman ME. Decidual vasculopathy and adverse perinatal outcome in preeclamptic pregnancy. Placenta 2012;33: 630–3. 19. Tache V, LaCoursiere DY, Saleemuddin A, Parast MM. Placental expression of vascular endothelial growth factor receptor-1/soluble vascular endothelial growth factor receptor-1 correlates with severity of clinical preeclampsia and villous hypermaturity. Hum Pathol 2011;42:1283–8. 20. Moldenhauer JS, Stanek J, Warshak C, et al. The frequency and severity of placental findings in women with preeclampsia are gestational age dependent. Am J Obstet Gynecol 2003;189:1173–7. 21. Turowski G, Berge LN, Helgadottir LB, et al. A new, clinically oriented, unifying and simple placental classification system. Placenta 2012;33:1026–35.
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22. Khong TY, Staples A, Bendon RW, et al. Observer reliability in assessing placental maturity by histology. J Clin Pathol 1995;48:420–3. 23. Grether JK, Eaton A, Redline R, et al. Reliability of placental histology using archived specimens. Paediatr Perinat Epidemiol 1999;13:489–95. 24. Leis Marquez MT, Rodriguez Bosch MR, Garcia Lopez MA. Clinical practice guidelines. Diagnosis and treatment of preeclampsia-eclampsia. Colegio Mexicano de Especialistas en Ginecologia y Obstetricia. Ginecol Obstet Mex 2010;78: S461–525. 25. Rı´os JM, Tufin˜o-Olivares E, Reza-Lo´pez S, et al. Birthweight percentiles by gestational age and gender for children in the North of Mexico. Paediatr Perinat Epidemiol 2008;22:188–94. 26. Lewis HS, Benirschke K. Overview of placental pathology and justification for examination of the placenta. In: Lewis SH, Perrin E, eds. Pathology of the placenta. 2nd ed. Philadelphia (PA): Churchill Livingstone; 1999:1–26. 27. Castellucci M, Kaufmann P. Basic structure of the villous trees. In: Benirschke K, Kaufmann P, eds. Pathology of the human placenta. 4th ed. New York (NY): Springer-Verlag, Inc.; 2000:50–115. 28. Medina-Lomelı´ JM, Medina-Castro N. Diferencias y similitudes de la preeclampsia y la hipertension gestacional. Ginecol Obstet Mex 2005;73:48–53. 29. Vrachnis N, Kalampokas E, Sifakis S, et al. Placental growth factor (PlGF): a key to optimizing fetal growth. J Matern Fetal Neonatal Med 2013;26:995–1002. 30. Leinonen E, Wathen KA, Alfthan H, et al. Maternal serum angiopoietin-1 and -2 and tie-2 in early pregnancy ending in preeclampsia or intrauterine growth retardation. J Clin Endocrinol Metab 2010;95:126–33. 31. Hirashima C, Ohkuchi A, Takahashi K, et al. Gestational hypertension as a subclinical preeclampsia in view of serum levels of angiogenesis-related factors. Hypertens Res 2011;34:212–17. 32. Tripathi R, Ralhan R, Saxena S, et al. Soluble VEGFR-1 in pathophysiology of pregnancies complicated by hypertensive disorders: the Indian scenario. J Hum Hypertens 2013;27:107–14. 33. Larsen LG, Clausen HV, Jonsson L. Stereologic examination of placentas from mothers who smoke during pregnancy. Am J Obstet Gynecol 2002;186:531–7. 34. Jauniaux E, Burton GJ. Morphological and biological effects of maternal exposure to tobacco smoke on the feto-placental unit. Early Hum Dev 2007;83:699–706. 35. Ogge G, Chaiworapongsa T, Romero R, et al. Placental lesions associated with maternal underperfusion are more frequent in early-onset than in late-onset preeclampsia. J Perinat Med 2011;39:641–52. 36. Sanin LH, Reza-Lopez S, Olivares ET, et al. Relation between birth weight and placenta weight. Biol Neonate 2001;80:113–17. 37. Egbor M, Ansari T, Morris N, et al. Pre-eclampsia and fetal growth restriction: how morphometrically different is the placenta? Placenta 2006;27:727–34. 38. Eskild A, Vatten LJ. Do pregnancies with pre-eclampsia have smaller placentas? A population study of 317 688 pregnancies with and without growth restriction in the offspring. BJOG 2010;117:1521–6. 39. Roberts JM, Escudero C. The placenta in preeclampsia. Pregnancy Hypertens 2012; 2:72–83.
ORIGINAL ARTICLE
Gabriela Ruiz-Quin ´ pez,1 ˜ onez,1 Sandra A. Reza-Lo Dora Virginia Cha ´ vez-Corral,1 Blanca Sa ´ nchez-Ramı´rez,2 Irene Leal-Berumen,1 and Margarita Levario-Carrillo1 1
Facultad de Medicina and Facultad de Ciencias Quı´micas, Universidad Auto´noma de Chihuahua, Chihuahua, Me´xico
2
Objectives: To compare maturity of placentas from women with hypertensive disorders with those from normotensive pregnancies and to determine the relationship between placental maturity (PM) and the diagnosis of small-for-gestational-age (SGA) in the newborns. Materials and methods: We examined placental stained specimens from women with normotensive pregnancies (n = 100), diagnosis of gestational hypertension (n = 38), mild (n = 10), or severe preeclampsia (n = 34) in an optical microscope. Placental Maturity Index (PMI) was calculated as the number of vasculo-syncytial membranes (VSM) in 1 mm2 divided by VSM thickness (mm). Hypermaturity was defined as >90th percentile of the PMI from placentas of normotensive pregnancies. Newborns were classified as SGA, adequate-for-gestational-age (AGA) or large-for-gestational-age (510th, 10–90th, and >90th percentile from weight for gestational age reference tables, respectively). Results: PMI in preeclamptic women (taking together mild and severe preeclampsia, PMI = 43.4 ± 1.6) was significantly higher than in normotensive women (PMI = 36 ± 2, p = 0.045). Hypermaturity was more frequent (p50.05) in placentas from women with preeclampsia than in those from normotensive women only in preterm pregnancies (537 weeks), but not in those at term (p = 0.41). The frequency of hypermaturity in placentas from women with gestational hypertension was not statistically different than in normotensive women. Hypermaturity was also more frequent in placentas from SGA (OR = 2.63, p50.05) than in AGA newborns. Conclusion: The PMI was increased in preeclampsia, but not in gestational hypertension. Placental hypermaturity was also associated with the diagnosis of SGA in newborns. PM might have a role in the relationship between maternal factors and SGA.
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Placental maturity, hypertensive disorders of pregnancy and birth weight
Keywords Birth weight, Gestational hypertension, Placental maturity, Placental maturity index, Preeclampsia, Small-for-gestational-age.
INTRODUCTION Hypertensive disorders of pregnancy, such as gestational hypertension and preeclampsia, are common and affect about 10% of pregnancies (1). They are
Correspondence: Sandra A. Reza-Lo´pez, Laboratorio de Embriologı´a, Facultad de Medicina, Universidad Auto´noma de Chihuahua, Circuito Universitario Campus II, Chihuahua, Chih. C.P. 31109, Me´xico. Tel: +52 (614) 439 1500, ext. 3572. E-mail: [email protected]
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Placental maturity and hypertensive disorders
the main cause of maternal mortality in developing countries and they are also associated with intrauterine growth restriction (IUGR), thus increasing perinatal mortality and morbidity (2–4). Several maternal, placental and fetal factors influence fetal growth and development. Maternal age, nutrition, body composition and complications during pregnancy have been associated with birth weight (5,6). Other factors related to preplacental, uteroplacental, or postplacental hypoxia, such as maternal anemia, preeclampsia or IUGR, respectively, also affect fetal growth. Because the placenta mediates nutrient transport between the mother and the fetus, the functionality of its structures plays a fundamental role for fetal growth and development (7,8). Placental morphology changes as pregnancy progresses. The proportion of syncytial knots, the number of terminal villi, and the number of vasculosyncytial membranes (VSM) gradually increase and VSM thickness decreases as the placenta matures. These changes in placental maturity (PM) are observed in placentas from non-complicated pregnancies from weeks 21 to 38 (9,10), after which PM shows a plateau (11). However, PM may be influenced by several maternal and fetal factors resulting in a delayed (hypomaturity) or accelerated PM (hypermaturity). For instance, gestational diabetes and Rhesus incompatibility have been associated with delayed PM (12), maternal smoking habit has been associated with both delayed and accelerated PM (12–14), and preeclampsia has been associated with an accelerated PM, in particular, in those with an early start of disease [33–56% in pregnancies before the 37th week vs. 4% in pregnancies at term, 37 weeks] (15–19). Furthermore, the degree of PM has been related with the severity of hypertensive disease in some studies (16,19,20). Placental accelerated maturity or placental hypermaturity (PHM) has been also observed in cases of IUGR low birth weight (15,17,18,20) associated or not with the diagnosis of preeclampsia (15). A hypermature placenta is characterized by the predominance of terminal villi and an increase in syncytial knotting, as compared to features expected for its gestational age (12). A standardized classification of placental pathology diagnosis based on its morphology has been proposed. However, there is no agreement in the literature regarding which indicator would be the best to define PHM and its relationship with clinical outcomes (21). PHM has been assessed using several measures and cut-off. For example, the number of syncytial knots above the average has been used as a marker of PHM. However, the average value was obtained from a small sample size [n = 9/10 per gestational week] (19). Other authors have assessed PHM by the predominance of small terminal over intermediate villi and syncytial knotting, but no cut-off was reported (20). Although these studies did not report the intra and inter-observer agreement, other studies have reported that the observer reliability of placental histological measures is poor (22). For example, interobserver agreement in villous maturity between five expert pathologists has been reported with a kappa value of 0.58 (23) and a kappa value 0.60 was obtained between two pathologists for the diagnosis of maturation disorders (21). Then, the placental maturity index (PMI) has been proposed as a more objective histological assessment.
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The PMI is correlated with gestational age and birth weight and takes into account the number of epithelial plates (or VSM) in terminal villi and their thickness because these two measures are directly related to PM (10). However, it is unclear whether the PMI is altered by hypertensive disorders of pregnancy and in IUGR. Therefore, the objectives of this study were: (1) To compare the PMI in placentas from women with diagnosis of gestational hypertension and preeclampsia with those from normotensive pregnancies; and (2) to determine the relationship between the PMI and the diagnosis of small-for-gestational-age (SGA) in the newborns.
MATERIALS AND METHODS Women either normotensive (n = 100) or with hypertensive disorders of pregnancy (gestational hypertension, n = 38; mild preeclampsia, n = 10; and severe preeclampsia, n = 34) were recruited from two public hospitals (Hospital General Salvador Zubira´n and Hospital Central del Estado, Chihuahua, Me´xico) for this cross-sectional study. Women with diagnosis of heart disease, neuropathy, pregestational hypertension, diabetes mellitus, hyper or hypothyroidism, eclampsia, HELLP syndrome, those with twin pregnancies, fetal death, and those with a newborn with congenital defects were not included in the study. Women accepted to participate by signing an informed consent form. The study protocol was approved by the institution ethics board. We obtained information on maternal clinical characteristics, biochemical measures and newborn anthropometry by questionnaire and from clinical records. Anemia was defined as hemoglobin concentrations 511.0 g/dl. Diagnosis of gestational hypertension, mild or severe preeclampsia was confirmed according to the Guidelines of the Mexican College of Obstetricians and Gynecologists (24). Briefly, gestational hypertension was defined as a systolic blood pressure of 140 mm Hg, or a diastolic blood pressure 90 mm Hg in women with previously normal blood pressure; mild preeclampsia was diagnosed when systolic and diastolic blood pressure were of 140 mm Hg or higher and 90 mm Hg or higher, respectively, after the 20th gestational week in women with previously normal blood pressure; and proteinuria (0.3 g protein in a 24-h specimen). Preeclampsia was considered severe when one or more of the following criteria were present: systolic blood pressure 160 or diastolic blood pressure 110 mm Hg on 2 occasions at least 6 h apart, proteinuria 2 g in a 24-h specimen or 3þ in 2 random samples at least 6 h apart, oliguria of less than 500 ml in 24 h; cerebral or visual disturbances; pulmonary edema or cyanosis; epigastric or right upper-quadrant pain, impaired liver function, thrombocytopenia, or fetal growth restriction (24). Gestational age was calculated from the date of last menstrual period and confirmed by ultrasound studies performed before the 16 weeks of gestation in 20% of the study population (intra-class correlation coefficient [ICC] = 0.89). Newborns were classified according to their birth weight and gestational age as small (510th percentile), adequate (10–90th percentile), or large (>90th percentile) for gestational age, using percentile reference tables of weight for gestational age for infants from the North of Mexico (25).
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Placental maturity and hypertensive disorders
Sample Collection and Morphometric Analysis of Placentas Immediately after birth, the umbilical cord was clamped, the maternal blood clot was removed, and the placenta collected. Placental weight and major and minor diameters were measured. A macroscopic examination was performed looking for areas of infarct, fibrin deposition and calcification (26). Placenta samples were obtained and analyzed as in previous studies (11). Briefly, samples from the central area of placentas were dissected from macroscopically lesion-free sites and were immediately fixed in a 10% formol solution, embedded in paraffin, and stained with hematoxylin and eosin. We examined stained specimens with an optical microscope (Axioscope 2 Plus, Carl Zeiss Jena GmbH, Jena, Germany), using the AxioVision software (AxioVision LE, v.4.6.2.0, Carl Zeiss MicroImaging GmbH, Germany) selecting the area of the slide without any microscopic lesion (or with the least number of lesions) for maturity measures. The number and average diameter of terminal villi [terminal villi were defined as those with diameter between 30 and 60 mm] (12) found in 1 mm2 were assessed. We obtained the average of 5 fields at a 5 magnification. In photomicrographies of each slide, we measured the following: number of VSM (identified in the external sites of the villi, as nuclei- and knotting-free areas), the thickness of VSM in the thinnest part of the transversely cut surface of the terminal villi and the diameter of capillaries, with a 40 magnification. The average of these measurements in 10 terminal villi was calculated. We calculated the PMI as the number of VSM divided by the average of their thickness (10). All placenta measures were carried out by an observer, blinded to the participant diagnosis. The values of ICC calculated to evaluate intra-observer agreement were: 0.88 for the VSM thickness, 0.97 for the number of VSM, and 0.98 for the number of terminal villi. Statistical Analyses Data are presented as means and standard deviation or frequency and proportion depending on the variable measuring scale, unless otherwise indicated. The sample size of the group with diagnosis of mild preeclampsia was small (n = 10), therefore we also carried out analyses taking together both mild and severe preeclampsia groups. Group means were compared by one-way ANOVA. Log-transformed variables or Kruskal–Wallis test were used when the variables were not normally distributed. Differences in variables measured in nominal scale were analyzed by 2 test or Fisher’s exact test. To evaluate PHM, we took as a cut-off the 90th percentile of the PMI distribution in the normotensive group with newborn AGA considering gestational age (preterm 537 week; term 37 weeks). The PMI cut-off was 53 for preterm pregnancies placentas, and 68, for those at term. Logistic regression models were used to determine the association between PHM and hypertensive disorders and with SGA outcome, and odds ratios (OR) were calculated. We tested the potential effect of other biological or statistically significant variables by multivariate analyses. Stata, v. 11.0 (Stata Statistical software, Release 11.0, College Station, TX: stata) was used for data analyses.
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RESULTS Characteristics of the studied groups were not statistically different, except in the number of years of education (Table 1). Table 2 shows the morphological characteristics of placentas by study group. The number of VSM was greater in placentas from the severe preeclampsia group, compared with the normotensive group. There was a trend towards a smaller diameter of terminal capillaries in placentas from the gestational hypertension group and a higher PMI in the severe preeclampsia group, compared with placentas from normotensive women. A higher proportion of placentas with infarct areas was observed in hypertensive disorders than in the normotensive group (Table 2). PMI in preeclamptic women (taking together mild and severe preeclampsia, PMI = 43.4 ± 1.6) was significantly higher than in normotensive women (PMI = 36 ± 2, p = 0.045). The correlation between the PMI and gestational age by diagnosis group was as follows: in normotensive women, r = 0.25, p = 0.01; in women with diagnosis of gestational hypertension r = 0.02, p = 0.92; and in women with preeclampsia, r = 0.34, p = 0.03. PHM was associated with early gestational age within women with preeclampsia; however, this relationship was not statistically significant in placentas at term (Table 3). Placentas obtained before week 37 from women with hypertensive disorders were characterized by a thinner VSM and an increased vascularity of terminal villi compared to placentas from normotensive women (Figure 1). Placentas from women with severe preeclampsia were more likely to have hypermaturity than those from the normotensive group. Similarly, placentas from newborns that were SGA were more likely to be hypermature compared to those from AGA newborns (Table 4). The magnitude of the association was similar and remained statistically significant, after adjusting the model for potential confounders, none of which resulted significant in the multivariate analysis. Newborns from women with severe preeclampsia were lighter at birth (median and interquartilar range [IQR], 2863 g [2313–3073 g]) than those born to normotensive women (3100 g [2729–3481 g]). Birth weight was not different in newborns from gestational hypertension and mild preeclampsia groups (3150 g [2894–3530 g] and 3280 g [3084–3528 g], respectively). Birth weight of newborns from women with severe preeclampsia and hypermature placentas was 2640 g (IQR 1310–2825 g) vs. 2975 g (IQR 2975–3155 g) in those without PHM (p = 0.045).
DISCUSSION The findings of this study partially support the hypothesis that hypertensive disorders of pregnancy increase PM. PHM was mainly found in placentas from women with preeclampsia but not in those with gestational hypertension. We also show that placentas from SGA newborns are more likely to be hypermature than those from AGA newborns. Consistent with others, we found that PHM is more frequent in women with preeclampsia. Tache´ et al. found PHM in 40 and 50% of cases of mild and
b
24 ± 7 20 (53) 18 (47) 39 ± 2 9±4 3 (8) 35 (92) 26 ± 4
40 (40) 60 (60) 38 ± 3 10 ± 3
8 (8) 92 (92) 24 ± 5
Mean ± SD/n (%)
Gestational hypertension, n = 38
23 ± 6
Mean ± SD/n (%)
Kruskal–Wallis test was used. Body mass index = weight/heigth2.
a
Maternal age (years)a Parity Primiparous Multiparous Gestational age (weeks)a Education (years) Smoking during pregnancy Yes No Pregestational BMIa,b (kg/m2)
Variable
Normotensive, n = 100
Table 1. Clinical characteristics of the studied groups.
1(10) 9 (90) 24 ± 3
7 (70) 3 (30) 39 ± 1 12 ± 5
22 ± 5
Mean ± SD/n (%)
Mild preeclampsia, n = 10
3 (9) 31 (91) 25 ± 6
20 (59) 14 (41) 37 ± 4 8±4
22 ± 6
Mean ± SD/n (%)
Severe preeclampsia, n = 34
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0.17
0.97
0.09 0.04
0.11
0.36
p
Placental maturity and hypertensive disorders
137
552 ± 113 19.9 ± 2.8 15.8 ± 1.9 38 ± 1 1.1 ± 0.1 19 ± 1 47 ± 2 16 ± 1 37 ± 1 7 (18) 31 (82) 7 (18) 31 (82) 1 (3) 37 (97)
7 (7) 93 (93) 20 (20) 80 (80) 3 (3) 97 (97)
Mean ± SD/n (%)
540 ± 130 18.0 ± 3.3 15.4 ± 2.7 36 ± 1 1.0 ± 0.1 19 ± 1 46 ± 2 18 ± 1 36 ± 2
Mean ± SD/n (%)
Gestational hypertension, n = 38
b
Variables were log-transformed for analyses and geometric means and SD are presented. p50.05 compared with normotensive group. c VSM = vasculosyncytial membrane. d Kruskal–Wallis test was used. e PMI = number of VSM/thickness of VSM (mm).
a
Weight (g) Major diameter (cm) Minor diameter (cm) Number of VSMc (villi/mm2)a Thickness of VSMc (mm) Number of terminal villi (in 1 mm2)a Terminal villi diameter (mm)d Terminal capillaries diameter (mm)a Placental maturity index (PMI)a,e Infarcts Yes No Fibrin deposition Yes No Calcification Yes No
Variable
Normotensive, n = 100
Table 2. Morphometric analysis of placental tissue of the studied groups.
0 (0) 10 (100)
0 (0) 10 (100)
2 (20) 8 (80)
628 ± 116 19.5 ± 2.7 17.1 ± 1.8 38 ± 1 1.0 ± 0.2 19 ± 1 46 ± 2 19 ± 1 38 ± 2
Mean ± SD/n (%)
Mild preeclampsia, n = 10
0 (0) 34 (100)
12 (35) 22 (65)
9 (26) 25 (74)
519 ± 150 17.9 ± 3.1 15.4 ± 2.6 46 ± 1b 1.0 ± 0.1 21 ± 1 46 ± 2 18 ± 1 45 ± 2
Mean ± SD/n (%)
Severe preeclampsia, n = 34
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0.86
0.08
0.01
0.13 0.32 0.17 0.01 0.69 0.32 0.52 0.07 0.06
p
138 G. Ruiz-Quin ˜ onez et al.
Placental maturity and hypertensive disorders Table 3. Placental hypermaturity by diagnosis group in preterm and term pregnancies. Placental maturity index
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Group Preterm pregnancies (537 weeks) Normotensive Gestational hypertension Preeclampsiaa Term pregnancies (37 weeks) Normotensive Gestational hypertension Preeclampsiaa a
90th percentile, n (%)
>90th percentile, n (%)
23 (92) 3 (100) 7 (50)
2 (8) 0 (0) 7 (50)
50.01
67 (89) 33 (94) 25 (83)
8 (11) 2 (6) 5 (17)
0.41
p
Including both, mild and severe preeclampsia.
Figure 1. Photomicrographs of central area tissue from preterm placentas (gestational age 537 weeks). Study groups: (A) normotensive, (B) gestational hypertension, (C) mild preeclampsia and (D) severe preeclampsia. Magnification of 5 (1) and 40 (2). VSM were identified as nuclei- and knotting-free areas in the external sites of the villi. The thickness of the VSM in the thinnest part of the transversely cut surface terminal villi and the diameter of capillaries were measured. VSM were more abundant and thinner in samples of placental tissue from hypertensive groups than in those from normotensive pregnancies. VSM, vasculo-sincitial membrane; Tvsm, thickness of vasculosincitial membrane; TV, terminal villous; V, villous vessels.
severe preeclampsia, respectively, compared to 12.7% in the control group (19) and Moldenhouer et al. (20) observed PHM in 32.9% of women with preeclampsia vs. 4.5% in normotensive women. In our study, PHM was found in 27% of placentas from women with preeclampsia and 10% in those from normotensive women. Differences in the magnitude of the reported proportions may arise from differences in the criteria and cut-off used to define PHM. Tache´ et al., determined PHM as those placentas with a syncityal knots number above the average (19), Moldenhauer et al. determined PHM according with the predominance of terminal villi over the intermediate villi and the syncytial knots number (20), and we used the 90th percentile of the PMI. In our study, the number of VSM was greater and a higher proportion of
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G. Ruiz-Quin ˜ onez et al. Table 4. Relationship between placental hypermaturity, hypertensive disorders and selected factors.
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Variable
PMI 90th percentile, n(%)
PMI >90th percentile, n(%)
Group Normotensive 90 (90) 10 (10) Gestational hypertension 36 (95) 2 (5) Mild preeclampsia 8 (80) 2 (20) Severe preeclampsia 24 (71) 10 (29) Gestational age (weeks) 537 33 (79) 9 (21) 37 125 (89) 15 (11) Smoking habit (number of cigarettes per day) 0 133 (88) 19 (12) 1–3 15 (94) 1 (6) 4 10 (71) 4 (29) Anemia Yes 19 (95) 1 (5) No 130 (86) 22 (14) Parity Primipaurus 71 (84) 14 (16) Multiparous 87 (90) 10 (10) Maternal age (years) 520 51 (88) 7 (12) 20–25 58 (87) 9 (13) 26 49 (86) 8 (14) Newborn small for gestational agea Yes 28 (76) 9 (24) No 119 (89) 14 (11) a
OR
CI95%
p
1.0 0.50 2.25 3.75
0.10–2.40 0.42–12.09 1.40–10.05
0.39 0.35 0.01
2.27 1.0
0.91–5.65
0.08
1.0 0.47 2.82
0.06–3.74 0.80–9.90
0.47 0.11
0.31
0.04–2.44
0.27
1.71
0.72–4.09
0.22
0.88 1.0 1.05
0.31–2.55
0.82
0.38–2.93
0.92
1.07–6.95
0.04
2.73 1.0
Excluding large for gestational age newborns.
VSM above the average number was observed in the group of severe preeclampsia. Because accumulation of nuclei is often observed directly lateral to the VSM (27), it is possible that the proportion of syncytial knots maybe related to the number of VSM, then we could speculate that their number might be also increased in placentas from preeclamptic women, but this remains to be confirmed. We also observed that the absolute number of terminal villi in 1 mm2 did not differ between groups. As the placenta matures, the proportion of terminal villi increases whereas the VSM thickness decreases. Thus, the PMI could be a precise indicator of villous maturity, because it takes into account the number of VSM of terminal villi and their thickness (10,11), in which the VSM thickness may serve as a proxy of VSM maturity. Furthermore, using the 90th percentile as a cut-off may identify the most severe cases of placenta hypermaturity. Further research is needed to compare these measures and to establish the most appropriate cut-off. The frequency of PHM in the group of gestational hypertension was not different from normotensive women. Although the reason for this is unclear, we could speculate that might be related to differences in the clinical course of hypertensive disorders. Whereas patients with gestational hypertension tend to present a benign evolution and similar perinatal outcomes than
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Placental maturity and hypertensive disorders
non-complicated pregnancies, patients with preeclampsia present a more severe clinical course, for both, the mother and the fetus, and they often have adverse perinatal outcomes (28). Differences in factors related to placenta growth and development, such as the vascular-endothelial growth factor, placental growth factor (PIGF), the soluble fms-like tyrosine kinase-1 (sFlt-1) and angiopoietins, might be also part of the mechanism explaining these differences. Women with low level of PIGF and high level of sFlt-1 exhibit alterations in placental development and have an increased risk of pregnancy complications such as preeclampsia (19,29,30). Alterations in these factors are less pronounced in women with gestational hypertension than in preeclampsia (31,32). However, the potential role of these factors to explain differences in PM in hypertensive disorders requires further investigation. PM has been related to several maternal factors, such as gestational age, maternal age, parity, anemia, and smoking habit, but none of them reached statistical significance in this study. However, there was a trend towards a higher proportion of PHM in preterm pregnancies (p = 0.08) than in those at term, and in placentas from women that smoked 4 cigarettes per day compared to those that did not smoke (p = 0.11). In the present study, we confirmed the correlation between gestational age and PMI only in the group of normotensive women but not in the groups with gestational hypertension or preeclampsia. This suggests that PM is altered in hypertensive disorders, and in particular in preterm pregnancies. This is further supported by the observation that PHM was found in 50% of placentas from women with preeclampsia in preterm pregnancies and only in 17% of placentas from women with preeclampsia who gave birth after 37 weeks. This finding is also consistent with other studies that have reported that PHM in women with preeclampsia is more frequent in preterm pregnancies than in those at term (15,18,20). Furthermore, an early start of hypertensive disorders could have been the reason for preterm birth (12,20) and may be related to characteristics of an accelerated PM. Several studies have shown that maternal smoking habit influences PM. However, the direction of this association has been inconsistent. For instance, some studies using the proportion of syncytial knots as a marker of PM have found degenerative changes and premature aging of placentas from women who smoke (13), similar to our observation that PHM tended to be more frequent in women who smoked 4 cigarettes per day. In contrast, other studies have found a decrease in vascularity and an increase on VSM thickness, which suggest hypomaturity, in placentas from women with smoking habit (14,33,34). As expected, an increased proportion of placentas from women with hypertensive disorders showed infarct areas. This observation is consistent with other studies that have reported higher proportion of infarct areas in placentas from women with preeclampsia or hypertension than in normotensive women (16,35). In this study, we also identified a relationship between SGA and PHM. Newborns born SGA had almost 3 times more possibilities of having PHM than those born with an adequate weight for their gestational age. Other studies have found a decrease in birth weight for gestational age in newborns from women with preeclampsia, but only in those that displayed accelerated
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PM features. In contrast, birth weight of newborns from women with preeclampsia in which PM was normal did not differ from birth weight of newborns of normotensive women (15–17). Our results showed that birth weight was lower in newborns from women with severe preeclampsia with or without PHM compared to those from normotensive women. However, newborns from women with preeclampsia and PHM were the lightest. Birth weight is closely related to placenta weight (36). In the present study, placenta weight from SGA newborns was 67 g lighter than in AGA newborns, after adjusting by gestational age. However, placenta weight was not different between normotensive and hypertensive groups. Other studies have found no difference in placenta weight between normotensive and hypertensive groups (37) and similar placental weight have been found in SGA newborns from women with or without preeclampsia (38). In contrast, other studies have found a low placenta weight associated to preeclampsia. In our study, PHM, but not placental weight, was related to both, small birth weight and preeclampsia, suggesting that hypertensive disorders could be associated with placental physiology without affecting its weight. However, whether or not intrauterine growth restriction and preeclampsia have additive or interacting effects on placental pathophysiology (39) warrant further investigation. Overall, the results of the study suggest that PM is altered in hypertensive disorders; particularly in placentas from women with diagnosis of preeclampsia and preterm pregnancies and that the PHM is associated with a decreased birth weight. However, the study has several limitations. First, we have small number of women with hypertensive disorders, in particular in the group of mild preeclampsia, which did not allow us to examine the PMI by gestational week and diagnosis, due to the reduced sample size; and second, gestational age was calculated from the last menstrual period and could lead to some misclassification. However, in the 20% of patients in which the ultrasound was available before the 16th gestational week, the sonographic and calculated gestational age had good agreement. In conclusion, the PMI and hypermaturity are increased in preeclampsia, but not in gestational hypertension. PHM is also related to a decrease in birth weight for gestational age. Whether accelerated PM mediates the relationship between maternal factors and pregnancy outcomes such as SGA requires further investigation. Longitudinal studies with a larger sample size to evaluate these associations in complicated and non-complicated pregnancies are necessary.
ACKNOWLEDGMENTS The authors wish to thank the Personnel of the ‘‘Hospital General Salvador Zubira´n’’ and the ‘‘Hospital Central del Estado’’ for their support in sample and data collection.
DECLARATION OF INTEREST The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.
Placental maturity and hypertensive disorders
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